Central locking playing up on 1993 Cav Diplomat

[mycav]

All 5 locks generally work normally when locked either on the driver's door or the passenger door. At some point the nsf lock stops working. It still makes the normal loud locking noise but the control knob only moves up or down a little, , when locked/unlocked with the driver's door key. The passenger side key will then unlock the car completely once... and then the system stops working. A minute later the controller starts working again, with or without the problem.
Much the same thing happens with the osr lock but when it's failed the locking sound is much quieter when trying to lock/unlock.
I checked the wiring for voltage and continuity. Everything was OK and the same voltage pulses went to each lock.
What can produce these intermittent failures?
Help!

[Cavalier342]

Well there's always the central locking module to check for dampness/connection faults. It's in the driver's footwell, behind the kickpanel just in front of the door. It's normal for the system to stop working if it's overloaded or if you unlock/lock too many times in a short space of time, usually around 10 times or so. Try a replacement module unit, there should be some on ebay knocking about.

[mycav]

Well, I have to say that the control unit looked dry and all wiring was sound. I tended to discount it after checking it over since the same lock/unlock pulses go to all 5 locks at the same time but 3 or 4 locks carry on locking and unlocking correctly. Unfortunately I know I can't discount it completely.
I accidentally jammed the nsf lock by over-tightening the door card. It squeezed the horizontal rod and completely stopped its movement. Loosening just one screw let it operate again. I carried on testing the lock while loosening the door handle screw and the noise the lock made when it started to work was very similar to the osr lock when it stopped working properly. But, would two locks fail with very similar problems?
At least the knobs of the faulty locks can be moved by hand so the MOT tester won't get locked in or out when its tested later this month!

[planetc]

sounds like iffy motors to me

[mycav]

I can't figure out if the motors are failing or the lock mechanisms are stiff or the rods are jamming somewhere. So I just bought a nsf lock to plug in and test how the complete mechanism works when a door harness plug's connected to it.
It looks like the same lock plug's used for nsf and osr and, although some pins aren't used on the back ones, the same 3 pins drive both lock motors in the same way. At least that's what Mr Haynes says!